1. Field of the Invention
The present invention relates to an apparatus, method, computer program and recording medium for processing information. More specifically, the present invention relates to an apparatus, method, computer program and recording medium for allowing content to be used by delimitation unit in the use of content recorded on an information recording medium.
2. Description of the Related Art
Digital versatile discs (DVDs) and Blu-Ray Disc (Registered Trademark) are currently used as recording media of content such as music and movies. Such information recording media contain a random-access memory (ROM) type medium that does not permit new data to be recorded and a recordable (R) or re-writable (RE) type medium that permits data to be recorded. Using a data rewritable information recording medium, a user may record content received via a network or broadcasting.
Creators or sellers of broadcast content, music data, image data, typically hold copyright and distribution right. When such content is distributed, certain limitations are imposed on the use of the content. Only an authorized user is permitted to use the content. For example, unauthorized copying is prohibited.
In accordance with one technique of imposing limitations on the use of content, content is encrypted and distributed, and only an authorized user or an authorized device is permitted to decrypt the encrypted content for use. Japanese Unexamined Patent Application Publication No. 2003-116100 discloses a technique of controlling the use of content, for example.
Advanced access content system (AACS) is available as standard related to content copyright protection technique based on encryption of content. In accordance with the AACS standard, the content is segmented into units, each unit is encrypted with a respective unit key, and the encrypted unit is then stored on a disk. A unit key file containing a unit key is recorded on the disk as a file containing encrypted unit key. Furthermore, a media key block (encryption key block) is recorded on the disk.
The MKB is an encryption key block that is generated in accordance with a tree-structured key distribution method known as one of broadcast encryption schemes. A media key Km can be acquired only through a decryption process in accordance with a device key Kd stored on an information processing apparatus of a user who has an effective license. Using the media key Km, an encryption unit key contained in the encrypted unit key file is decrypted. The unit key is thus obtained. Using the unit key, the encrypted content is decrypted.
The content is segmented into units, and the units are encrypted with the unit keys different from unit to unit assigned thereto. The use of the content is thus controlled on a per unit basis.
A variety of types of information processing apparatuses and content recording media are available. For example, the recording media include a read-only memory (ROM) type medium permitting only data reproduction, and recordable type (R type) and re-writable type (RE type) media permitting data to be written. The information processing apparatuses using content also include a reproducing only apparatus, and a recording and reproducing apparatus.
A variety of apparatuses and media currently available allows content to be used in a variety of applications. For example, the ROM type disk is free from recording of new content or deletion of recorded content, the content or key information recorded on the disk is fixed and not updated. On the other hand, in the R or RE type medium permitting data to be rewritten, the content recorded on the disk is not fixed. New content may be recorded, and recorded content may be deleted or updated. Along with data updating, a unit key may be added or deleted.
New content may be recorded on a disk in a variety of methods. For example, broadcast content may be recorded on a real-time basis, or content may be downloaded from a content server. In this way, there is a variety of types of information processing apparatuses and media, and content is used in a variety of methods. There is a need for performing an optimum usage control for a variety of content usages.